It has long been known that aluminum tends to corrode in the presence of high voltage AC electrical fields. This has placed a limitation upon the use of metallized film capacitors using aluminum for their electrodes.
Efforts to solve this problem are represented, for example, by Forster U.S. Pat. Nos. 4,190,878 and 4,305,111. The first of these uses plastic sheets, such as polypropylene, coated with aluminum containing a small percentage of copper. The other adds Ni, Mg, Ti, Hf, or Be to the aluminum electrode. Similarly, British patent 1,546,354 forms electrodes from a coating of aluminum with another metal having a low specific resistance, such as Cu, Zn, Mn, Sn, Cr, Fe, and Pb. This work was directed at the use of semiconductive oxides which when formed reduce the high field associated with the edge of the corrosion sites and thus self heals the corrosion process. By contrast, my capacitor corrodes little, if at all, and, so, does not need to be self-healing.
My electrode of my capacitor controls the pH in the vicinity of the aluminum oxide thus preserving its protective qualities and so prevents corrosion of the elemental aluminum, rather than, as in the past, using a combination of metals which serve to heal the corrosion after it has occurred.